Postweaning multisystemic wasting syndrome (PMWS) is a newly emerged disease of pigs. PMWS appears to destroy the host immune system and causes a high mortality rate in weaned pigs. This disease has a long incubation period, typically 3–8 weeks, and affects many organs of infected pigs. The PMWS syndrome detected in Canada, the United States and France is clinically characterized by a gradual loss of weight and by manifestations such as tachypnea, dyspnea and jaundice. From the pathological point of view, it is manifested by lymphocytic or granulomateus infiltrations, lymphadenopathies and, more rarely, by hepatitis and lymphocytic or granulomateus nephritis (Clark, Proc. Am. Assoc. Swine Prac. 1997; 499–501; La Semaine Veterinaire No. 26, supplement to La Semaine Veterinaire 1996 (834); La Semaine Veterinaire 1997 (857): 54; Gupi P. S. Nayar et al., Can. Vet. J, vol. 38, 1997; 385–387). PMWS-affected piglets often die from respiratory failure and interstitial pneumonia with histiocytic cell infiltration.
Porcine circovirus (PCV) causes worldwide infection in swine and is highly contagious. PCV was originally detected as a noncytopathic contaminant of porcine kidney (PK15) cell lines. PCV has been classified into the new virus family Circoviridae. These viruses are small, nonenveloped agents with a single-stranded circular DNA genome.
A variety of circoviruses have been identified in a range of animal species including PCV, chicken anemia virus (CAV), beak and feather disease virus (BFDV) of psittacine birds, plant viruses including subterranean clover stunt virus (SCSV), coconut foliar decay virus (CFDV) and banana bunch top virus (BBTV). There do not appear to be DNA sequence homologies or common antigenic determinants among the currently recognized circoviruses. Todd et al. (1991) Arch. Virol. 117:129–135.
Members in the circovirus family have been shown to cause anemia, immunodeficiency-related diseases and to infect macrophage cells in vitro. PCV has only recently been implicated in PMWS. See, e.g., Ellis et al. (1998) Can. Vet. J. 39:44–51 and Gopi et al. (1997) Can. Vet. J. 38:385–386. However, the etiologic association of PCV with PMWS has been questioned due to the ubiquitous presence of PCV in the pig population. Additionally, experimental infections of pigs with PCV inocula, derived from contaminated PK15 cell cultures, have failed to produce clinical disease. See, e.g., Tischer et al. (1986) Arch. Virol. 91:271–276.
Infectious agents of swine, especially viruses, not only profoundly affect the farming industry, but pose potential public health risks to humans, due to the increased interest in the use of pig organs for xenotransplantation in humans. Previous diagnosis of PMWS disease has been based on histopathological examination. Accordingly, there is a need for improved methods of diagnosing the presence of PMWS-associated pathogens, as well as for preventing PMWS disease.